1. Field of this Invention
This invention relates to the field of drilling gas, oil, water and/or steam wells.
2. Prior Art
In the early days of drilling oil and gas wells, the wells were often drilled by cable tool. That technique involved a sharp weight on the end of a cable that pounded its way into the earth. Hydrocarbons often spewed from the well hole. The modern technique is to drill using a rotary drill, i.e., turning steel knuckles or teeth (on tungsten), located on the drill pipe.
Drilling mud is a fluid that cools the drilling bit (or teeth) while transporting rock cuttings to the surface. The mud also serves to keep any oil or gas underground.
In more detail, most modern drilling is done by means of rotary drilling. The drill bit rotates while bearing down on the bottom of the well, thus gouging and chipping its way downward. When conducting rotary drilling, the well bore is kept full of liquid during drilling. A weighted fluid (called drilling mud) in the bore hole serves at least two important purposes: (a) by its hydrostatic pressure, it prevents the entry of formation fluids into the well thus preventing blowouts and gushers; and (b) the drilling mud carries the crushed rock to the surface, so that the drilling is continuous until the bit wears out. The drill bit is connected to the surface equipment through a drill pipe, a heavy-walled tubing through which the drilling mud is fed to the bottom of the bore hole. In most cases, the drill pipe also transmits the rotary motion from a turntable at the surface to the drilling bit at the bottom of the hole. The top piece of the drill pipe is a tube of square or octagonal cross section called the kelly, which passes through a square octagonal hole in the turntable (located near the bottom of the derrick). At the bottom end of the drill pipe are extraheavy sections called drill collars that serve to concentrate the weight on the rotating bit. The drilling mud leaves the drill pipe in such a way that it washes the loose rock from the bottom and carries it to the surface. The drilling bit has a number of jets through which the drilling mud is forced by pressure into the bottom of the drill hole. Drilling mud is carefully formulated to the correct weight and viscosity characteristics for its required tasks. After screening to remove the rock chips, the returning drilling mud is held in open pits for recirculating through the well. The drilling mud is picked up by piston pumps and forced through a swivel joint into the top of the drill pipe.
The characteristic tall derrick contains the hoisting equipment that is used to raise and lower the drill pipe into the well. The drill bit wears quickly and requires frequent replacement, making it necessary to pull the entire drill string from the well and rack it at one side of the derrick. Joints of drill pipe are usually 30 feet long. Sections of two or three such joints are separated and racked vertically while the bit is being changed. Drilling mud is left in the bore hold during this time to prevent excessive flow of fluids into the well.
In drilling wells it is sometime desirable and necessary to reverse the circulation of the drilling fluid through the drill pipe and annulus. (The annulus is the region between the well casing or side and the drill pipe.) Presently, this is done through the open annulus which does not allow for rotation of the drill pipe while reverse circulating the drilling fluid.